LX'er have had a chat with Simon Law, the newly hired Quality Controller at Canonical – the company behind Ubuntu.
The interview is found here

Quote:

How do you decide when to fix a bug, and when to kick a bug report upstream?

We do our best to link all relevant bugs with the upstream software developers. It's all part of being a good citizen in the free software and open source world.

Whenever we encounter a bug with a piece of code we haven't written, our bug triagers go searching in the upstream bug tracking database. If they find a bug that's already there, great!Our bug tracking system, Malone, is designed to track the status of that bug. We'll put a link to the corresponding Ubuntu bug so that upstream developers can track our progress.

Then it's up to the developers to decide when to resolving a particular bug. If it affects our users, we'll commit resources to fixing it then and there.